36 LABORATORY OUTLINES FOR EMBRYOLOGY 



the cavities of the ventricles but the walls are very much 

 thinner. The two auricles are separated dorsally by a 

 thin membrane, the septum spurium. They are sepa- 

 rated ventrally by a thicker membrane, the continuation 

 of the ventricular septum. 



Draw the section, color the germ layers, and label all the 

 parts. 



(4) Through the Body about Half Way between the Fore-limb Buds 

 and the Hind-limb Buds 



This section passes through the umbilical cord. The 

 description of the spinal cord given in section (2) will 

 apply here. The dorsal aorta is a single vessel in this 

 region. On either side of the dorsal aorta is a large body 

 filled with holes. These bodies are the Wolffian bodies. 

 The part of the digestive tract in this region is the 

 stomach. It is connected to the body dorsally by a neck 

 of mesoderm, the major omentum. The mesoderm con- 

 tinuing from the stomach ventrally is the minor omentum. 

 Surrounding the stomach laterally and ventrally are 

 four large lobes of tissue filled with holes. These masses 

 of tissue are the lobes of the liver. The large blood 

 vessel in the right dorsal lobe is the inferior vena cava. 

 The large blood vessels in the ventral lobes are the um- 

 bilical veins. In the tissue between the liver lobes is a 

 hole surrounded by a thickened wall, the gall-bladder. 

 Identify the umbilical arteries in the umbilical cord. On 

 the ventro-median surface of the Wolffian body, near the 

 dorsal end of the major omentum, is a ridge, the genital 

 ridge. 



